It is well understood by those skilled in the art of weaponry that firearms typically fall into two separate families, those being: smooth bore and rifled bore. A smooth bore was the original design of all early firearms (cannons and hand held guns) smooth bore barrels fire mono- or multi-projectile shot without inducing a spin. The most recognized non-spinning mono projectiles would be fired from a colonial smooth bore musket, (i.e., the sphere configuration dominated in popularity and then the min-ball (a more aerodynamically shaped version)). Due to the advent of the second member of the firearm family, the rifled barrel, a superior method of firing a mono-projectile with a predictable flight path was achieved and the practice of firing slugs form a smooth boor is all but forgotten.
In contrast, most modern marksmen frequently use smooth bore barrels to fire non-spinning multi-projectile shot as buckshot or birdshot, which are most often referred to as “scatter shot” due to the reliance on random events/influences to cause a spreading out of the plurality of projectiles. This shot type was originally referred to as “scatter-shot” because it relies on random influences (e.g., wind, barometric pressure, temperature, velocity, collisions, turbulence, etc.) to achieve a random but semi-predictable rate/pattern of ever expanding separation. As the plurality of projectiles travel down the barrel of the gun and further travel down range toward the target, the spreading out of the projectiles occurs randomly and simultaneously on all three axes X,Y,Z (vertical, horizontal and depth). Because of the three axes random separation, this type of shot is most effective only at semi-close range engagements of 10 to 40 yards. Unfortunately, under ten yard the spread pattern is nominal and offers little advantage if any over a mono-projectile, and beyond 40 yards large gaps between projectile segments develop unpredictably thereby reducing probability as they continue to spread indefinitely.
As marksmen became increasingly frustrated with the limitations of the predictability of flight paths (accuracy) of mono-projectiles fired from smooth bored firearms, rifled bore firearms were created. Barrel rifling is a relatively simple modification to a standard gun barrel but the effects of the rifling resulted in a quantum leap forward in improving the predictably of the flight path of a mono-projectile fired from it; the accuracy benefit is due primarily to the gyroscopic stabilization gained as a result of spin imparted to the projectile as it contacts the grooves and lands of the rifling pattern while the bullet travels the length of the barrel. To clarify, the improved predictability (accuracy) is achieved by imparting a spin to the projectile as it rubs against the riffling in the barrel prior to it leaving the tip of the gun. This spin gyroscopically stabilizes the projectile as it travels down range.
The rifled bore group of firearms is commonly divided into four sub-categories: 1) Small caliber weapons using ammunition ranging in size from 0.22 inch which are commonly fired from small handguns; 2) Small arms weapons which use straight sided centre fire ammunition, the ammunition being fired from handguns and semi-automatic guns, the common bores being 0.38 inch, 0.357 inch, .45 cal, 0.44 inch, 9 mm and 10 mm which offer accuracy over a range up to 50 meters; 3) Combat rifles which fire ammunition sending projectiles at very high velocities over ranges of 500 meters plus, the common bores being 0.223 inch (5.56 mm), 5.7 mm, 0.303 inch, 7.62 mm and 0.50 inch; and 4) Heavy weapons for firing ammunition up to 2 kilometers commonly having bores of 20 mm, 30 mm and larger, and which are used in extreme range combat to deliver large payloads.
While the spin-rates, muzzle velocities, bore diameters, and other parameters of the above-mentioned four sub-categories of rifled firearms vary from firearm to firearm, there is one common theme among the design of these firearms—all rifled fireams are designed to deploy a single spinning projectile that is designed to remain whole, and not materially expand or distort from it aerodynamic shape (regardless of the amount of centrifugal force exerted on it) until it collides with a target.
Since smooth bore and rifled firearms both have design advantages and disadvantages, one type of firearm may be preferable for a certain situation (e.g., shotguns may be desirable in mid-range engagements, 20 to 100 feet (combat or hunting of pray) whereas another type of firearm may be preferable for other situations (e.g., rifled firearms such as pistols may be desirable for ultra-close range engagements of 0 to 20 feet or long barreled riles may be desirable for long range engagements of 100 yards and beyond). However, since it is often impracticable or impossible to carry/use multiple types of firearms at the same time, most people are automatically limited by the type of firearm which they are carrying, and in turn they are further limited by the type of shot they can fire.